Single unit recordings will be made from alert macaque monkeys while fixational eye movements are monitored with a double-Purkinje image eyetracker. The lateral geniculate nucleus and the striate cortex will be studied. Spatial tuning curves of single neurons will be compared with already published human psychophysics done with the same stimuli. Contrast sensitivities will be determined using sinusoidal grating patterns and Fourier analysis. Effects of mean luminance level and temporal transients will be investigated. Neurons will be tested for sustained/transient, X/Y and color class. Effects of eye movements and the shift effect will be investigated and compared.